Cryptosporidium and Isospora are known as one of the main cause of diarrhea in both immunocompetent and immunocompromised subjects, all over the world. Incidence of enteropathogens such as Cryptosporidium spp. and Isospora belli considerably has increased, since immunodeficiency virus (HIV) rapidly disseminated. In addition, cancer patients are highly susceptible to opportunistic infections. This study aimed to estimate the prevalence of cryptosporidiosis and iso-sporiasis in immunocompromised

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... atients in Tehran. Methods: This study carried out on patients admitted to Imam Khomeini hospital during 2013-2014. Stool samples collected from 350 immunocompromised patients. Formol-ether concentration was performed for all stool samples. Zeil-Neelsen technique was applied to stain the prepared smears and finally, all slides were examined by light microscope. Results: Out of 350 patients, 195 (55.7%) and 155 (44.3%) were male and female, respectively. Cryptosporidium oocysts were detected in 3 (0.9%) samples including one sample from HIV+/AIDS patients and 2 samples from organ transplant recipients. Isospora oocysts were detected in 4 (1.1%) samples consisting 2 HIV+/AIDS patients, one patients suffering from malignancy and one patients with other im-munodeficiency diseases. Conclusion: Cryptosporidium sp, and I. belli are the most prevalent gastrointestinal parasitic protozoans that infect a broad range of individuals, particularly those patients who have a suppressed or deficient immunity system.